Field of the Invention
This invention relates to a motorcycle wherein a gear case which has a drive shaft driven by a power unit and in which gear wheels for transmitting rotation of the drive shaft to a rear wheel are accommodated is provided sidewardly of the rear wheel and the gear case includes a breather path which opens the inside of a gear chamber to the atmosphere.
Description of Background Art
Motorcycles include a drive shaft driving wherein driving force of a power unit is transmitted to a rear wheel (driving wheel) through a drive shaft. A gear case in which gear wheels for transmitting rotation of the drive shaft to the rear wheel are accommodated is provided sidewardly of the rear wheel.
Some vehicles of this type include oil for lubrication that is accommodated in the gear case and includes a breather mechanism for keeping the pressure in the gear case to a predetermined pressure. See, for example, Japanese Utility Model Publication No. Hei 2-393 and Japanese Patent Laid-Open No. 2008-75732.
In addition, not only air in the gear case but also lubricating oil in the gear case sometimes enters a path of the breather mechanism. It is desired to separate this oil and the air from each other so that only the air is communicated between the inside and the outside of the gear case.
However, in the breather mechanism as disclosed in Japanese Utility Model Publication No. Hei 2-393, a chamber which communicates the external air with the inside of the gear case is provided in the gear case body, and a communicating path extending obliquely upwardly is formed in a case cover which closes up a rear wheel side opening of the gear case body such that the chamber is communicated with the internal space of the gear case through the communicating path. Therefore, if oil enters the path, then the path along which air passes becomes narrower and the oil is sometimes discharged to the outside together with the air. As a countermeasure, the size of the chamber has been increased. Therefore, it is necessary to increase the size of the gear case.
Meanwhile, in the breather mechanism disclosed in Japanese Patent Laid-Open No. 2008-75732, a short breather hole extending in a substantially horizontal direction is formed in an upper portion of the gear case such that it is open to the external air through the breather tube. Therefore, the path along which the air is to pass is narrowed. Also in this instance, the oil is sometimes discharged to the outside together with the air. Thus, in order to increase the size of the path along which air is to pass as a countermeasure, it becomes necessary to increase the size of the gear case.